The present invention relates to a solid-state image sensing device, i.e., a device that converts light into electrical signal, especially a non-linear image sensing device whose conversion characteristic is compressive.
Solid-state image sensing device can be very small, light-weight and consumes less power. It has further advantages such that it is free from distortion in the image field and robust against sticking, vibration or strong external magnetic field. Since the solid-state chip can be manufactured by the same or similar process as that of general LSIs (Large Scale Integrated circuits), it can be mass-produced with high reliability. Thus, solid-state image sensing devices are widely used in many fields: for example, a linear image sensing device is used in a tele-facsimile machine and a two-dimensional image sensing device is used in a video recorder.
One of few shortcomings of the solid-state image sensing device is that the dynamic range is relatively small compared to the normal chemical photographic film using silver salt. This necessitates a subtle control of the exposure (light amount inputted into the solid-state image sensing device). Even using a sophisticated exposure control, there are sometimes the case where the dark part of the image is sensed completely black and the bright part of the image is sensed completely white (the output from the image sensing device saturates).